In apparatus of the type in which a condensor is disposed above the evaporator and connected by a conduit to a sealed condensable coolant, a coolant gas vaporized by the latent heat of gasification in the evaporator is fed upward to the condensor by the increasing pressure caused by the gasification and the coolant gas is then condensed by discharging the latent heat, and the condensed coolant liquid is caused to flow downward into the evaporator under the force of gravity as a mode of circulation of the coolant.
Accordingly, it is unnecessary in such apparatus to provide a circulation pump, whereby the apparatus can be of simple construction and a large quantity of heat can be effectively transmitted with a small difference of temperature as the phase transition of coolant is utilized. An important element can thus be electrically insulated by using an electrically insulative coolant. Thus, large quantities of power can be treated by a small portion, advantageously. Accordingly, such arrangements are especially suitable for cooling large capacity semiconductor devices which require high efficiency of transmission of heat and radiation of heat out of the apparatus.
FIG. 1 shows an example of the conventional apparatus which is applied as a heat transferring apparatus utilizing such phase transition of a coolant for cooling a semiconductor device. In this embodiment, the reference numeral 1 designates a stack having the structure of a heat generator, such as a semiconductor device equipped with a radiator, which is disposed within an evaporator 2 being sealed by a coolant liquid 3 at a level therein above the stack 1. A condensor 4 is placed above the evaporator 2, being connected by a conduit 5 to the evaporator. Radiation fins 6 for effectively radiating heat out of the apparatus are connected to the exterior regions of the condensor 4. A sealed terminal 7 is provided for electrically connecting the stack 1 to a suitable power source.
Thus, in the conventional apparatus disclosed, the coolant gas is vaporized by absorbing heat generated from the stack 1 in the evaporator 2 and is fed through the conduit 5 upward to the condensor 4, as shown by the dotted arrow line 8, by increasing pressure caused by the gasification in the evaporator, and the heat is discharged by the coolant gas contacting the wall of the condensor so as to be consensed to a liquid phase. On the other hand, the condensed coolant liquid is then returned by flowing down along the wall of the conduit 5 to the evaporator as shown by the full arrow line 9, so that it may be used again for cooling the stack 1. The vaporization and condensation steps are repeated by maintaining the thermal transferring function by the phase transition.
However, the natural circulation of the coolant can be smoothly performed only when the quantity of heat is relatively small. The natural circulation cannot be smoothly performed when the quantity of heat being transferred is increased. Thus, the coolant gas and the coolant liquid are counter-currently passing through the conduit 5, as shown by the arrow lines 8 and 9. Accordingly, the coolant liquid is essentially being pushed back to the condensor side by a friction contact occurring between the down flowing coolant liquid and the upflowing coolant gas. Moreover, the coolant liquid becomes clogged in the conduit 5 so as to disturb the upward passage of the coolant gas, wherein a partial heat-exchange takes place in the conduit, so as to prevent the best flow down of the coolant liquid, and thus, to defeat the primary function of the heat transferring apparatus.
The trouble is readily caused even when transferring smaller quantities of heat, depending upon the length of the conduits or curves, a step or a dead end of the conduit. In order to overcome such trouble, the condensor is disposed as close as possible to the evaporator and they are connected in vertical relation with a thick conduit or the coolant liquid is returned back through a different conduit so as to be completely separated from the coolant gas. However, such application or construction is limited and the apparatus becomes disadvantageously complicated and expensive.
As stated above, the heat transferring apparatus utilizing natural circulation and the phase transition of a coolant has various advantages, however, such troubles as discussed have prevented really practical application thereof.